Another Dyno Day in So Cal-this Saturday

[v6spider]

Guy: Is this due to the design of the valve-train as the cam rides directly on top of the valve? I think in pushrod engines this may not be as critical(But should not be overlooked). I am way more educated in those type of valvetrains then the Twin Cam design...anyway your experiance is way appreciated...I am always willing to learn.

Rob

[guycroft]

No, it's nothing to do with the fact that the cam is direct acting ie: has rocker ratio of 1:1

A rocker valve train will develop valve lift in exactly the same way as a direct-acting one except that the cam lift is much lower and one relies on the mechanical advantage of the rocker mechanism. If the cam lift integral is hopeless so will be also the lift characteristic at the valve.

G

[v6spider]

No, it's nothing to do with the fact that the cam is direct acting ie: has rocker ratio of 1:1

A rocker valve train will develop valve lift in exactly the same way as a direct-acting one except that the cam lift is much lower and one relies on the mechanical advantage of the rocker mechanism. If the cam lift integral is hopeless so will be also the lift characteristic at the valve.

G

That makes sense... The Rocker arms on a Chevy small block v8 have a ratio of 1.52:1. So the profile of that particular cam is not going to be as aggressive to get the lift your are seeking. Where as in the TC the ratio is stuck @ 1:1 therefore the cam profiles for high lift are going to be way more aggressive. Thus more wear and tear on the valve-train.

Thanks Guy!

Rob

[guycroft]

More wear and tear? Not so.

The wear on some rocker actuated setups can be worse, per-se, because of the shifting effect of the rocker on the valve tip. The TC Fiat has buckets which virtually eradicate that.
Moreover the wear on rubbing surfaces of cam, pushrods (if used) and rockers with either setup is primarily (though not solely) dependent on the spring poundage. A rocker valvetrain may need heavier springs than a direct-acting because of the weight of the extra moving parts though there is no hard and fast rule, there are some clever rocker layouts out there! And in the case of some (non-roller) rocker setups the friction is colossal compared with a direct acting bucket and friction causes,well, wear!

G

[v6spider]

Guy: In my case for my 4.3L Chevy v6 with vortec heads I am using roller tip rockers and hydraulic roller lifters - very low friction. The lift @ the valve is .525" and the duration is 290 degrees on a 114 degree lobe center. The Cam ramp profile is designed specifically for the roller lifters and the valves were setup with the correct spring pressure and pocket depth to allow for the change in lift without coil bind. The pressed in rocker studs were also replace with screwed in studs.

Cheers!

Rob